Infection with human herpes viruses results in an initial round of productive infection followed by life long persistence of the virus in various cellular reservoirs. Subsequently, virus can be reactivated from the latent state resulting in another round of productive infection. The interactive relationship between virus and host controls expression from the virus genome and results in either activation or repression of virus gene expression. Once activated gene expression is coordinately regulated in a temporal fashion. Regulated expression of the virus genome depends on the synthesis of virus gene products and their interaction with host proteins. These interactions control the transcription of virus genes. The two specific aims described in this application are designed to dissect the mechanism of this interactive control circuitry to determine how it is orchestrated. Our approach to this problem is to identify and characterize host and virus transacting factors and their cognate cis-acting sites using a combination of genetic and biochemical approaches. We propose to characterize sequences found in the promoter and leader regions of both beta and gamma genes to identify the regulatory sequences which are required for their interaction with virus and host factors and ICP4, the major regulatory protein of the virus. An additional series of experiments are described which will investigate the requirement for ICP27 expression and translocation in regulation of virus gene expression. The second specific aim is designed to characterize, in detail, a novel transcription unit in HSV-1 that crosses the joint region which segregates the two unique regions of the virus genome. We have identified novel transcripts that arise from this region and now propose to map these and determine their coding potential. These studies are designed with the express purpose of elucidating their function. Included in these analyses are experiments characterize a DNA sequence that has all the characteristics of a virus prom(,ter but fails to respond to virus infection. The putative promoter will be mutated and fused to a reporter gene and the various mutants will be place in the virus genome at ectopic sites to determine the effects of mutation to this sequence.